I think the problem you are having is bump-steer. This is due to poor suspension design rather then a crappy steering rack. Bump steer is caused when the lower control arm travels in a differn radius then the steering link.
Lets say that the lower control arm travels in a "C" shaped radius. And the steering link also travels in a "C" shaped radius. But the two radii are offsetted to a certain degree that causes the top parts of the two radii to meet at the top and the bottom parts of the radii to be far apart. ( I know this is hard to follow) so i drew a Picture
What this shows is that when ever your suspension travels up the steering will want to turn inwards because the streering link is physically being pushed in by the control arm, and visa versa.
One way to solve this problem is to lower the steering link with some sort of arm type thing that lowers the linkage.
How do you get the linkage? No idea. Hopefully someone can answer this for me